CBCT Scan Analyzes The Setup Error In Intensity Modulated Radiation Therapy

Objective:To analyze the setup error for Radiotherapy planning withIntensity modulated radiation therapy to calculate CTV safety margins ofPTV based on pre-treatment CBCT scan.Methods:Two hundred and eighty-eight patients For intensitymodulated radiation therapy by Vrian IX-4702Linear accelerator werescanned by cone beam CT before the first radiotherapy and afterwardonce a week to record the translational data of different parts of the tumorin X(left-right)， Y(ventral-dorsal)， Z(cranial-caudal) dircetions,calculate and analyze the first setup error.Results: The first setup error in X,Y and Z directions were(0.103±1.780)mm、(0.505±1.306)mm、(0.318±1.657)mm for head andneck cancer;were (0.088±2.526)mm、(-0.475±3.384)mm、(1.464±3.092)mm for pelvic cancer.Conclution:Through the Analysis of setup error from this group ofCBCT scan, recommends the margin are3mm into3directions for headand neck cancer;which are6mm in X,Z directions,7mm in Y direction forpelvic cancer.